docs: def _field_names_(self):
          """ get list of field names defined in Swagger spec
  
          :return: a list of field names
          :rtype: a list of str
          """
          ret = []
          for n in six.iterkeys(self.__swagger_fields__):
              new_n = self.__swagger_rename__.get(n, None)
              ret.append(new_n) if new_n else ret.append(n)
          
          return ret